Proportioning control system



Jly 7, 1953 A. cLARKsoN PROPORTIONING CONTROL SYSTEM Filed June 1. 1 950 Patented July 7, 1953 UNITED STATES PATENTOFFICE PROPORTIONING CONTROL SYSTEM Alick Clarkson, Itasca, Ill., assignor of one-half to Vapor Heating Corporation, Chicago, Ill., a corporation of Delaware Application June 1, 1950, Serial No. 165,428

9 Claims. 1

This invention relates to improvements in boiler control systems.

In the normal operation of the boilers of steam generators conditions usually arise which vary the demand for steam. As the demand for steam is increased, the supply of feed water must be correspondingly increased, as also the delivery of fuel to the heating apparatus, in order'to prevent a drop in pressure and the quality of the steam. Conversely, as the demand for steam is decreased the supply of feed water must be correspondingly decreased with a decrease in delivery of fuel, otherwise the quality of the steam will be lowered during periods of reduced consumption when less fuel is required. It will thus be apparent that itis highly desirable and especially in a water tube boiler to automatically maintain a proportional balance between the delivery of feed water to the boiler, the delivery of fuel to the heating apparatus, and the discharge of steam.

The invention includes the use of conduits provided with orifice fittings and therefore, broadly considered, takes into account the physical laws governing the flow of fluids through metered orices and utilizes the associated physical phenomena to automatically proportionally control the flow of one or more fluids, for example, the delivery of fuel to a boiler heating apparatus in relation to the delivery of feed water tothe boiler. In carrying out my invention I employ a restricting orifice in the pipe line for delivering feed water into a boiler and also in a pipe line for delivering fluid fuel to the apparatus for heating the boiler. The pressure differential on opposite sides of the orifice fittings is utilized to operate means for controlling the delivery of said fuel in relation to the delivery of feed Water. In this Way I am enabled to accurately control the steam generating or uid heating function of a boiler by energizing controls at the intake end of the boiler rather than from the discharge end. While it may be possible to use similar means for proportionately controlling the delivery of feed water and the delivery of fuel in relation to the outflow of steam or hot Water from the boiler, I prefer controlling the output in relation to the intake. This is particularly true in connection with boilers of the water tube type', sincethe control of the intake and fuel minimizes variations in the quality of steam discharged from the boiler. In order to further increase the accuracy of my control system, I have provided means which is responsive to the temperature of the steam and/or other fluids discharged from the boiler. The said temperature responsive means isinterconnected withy the pressure controlled means and operable 2 concurrently therewith, to adjust the relative positions of the associated proportional mechanism to take into account the temperature of the fluid discharged. Also as a further alternative to the temperature responsive adjustment, similar means are shown, whereby manual adjustments may be readily and conveniently made.

The proportional control herein shown can obviously be `extended to proportionately control the flow of fluid streams in other situations. Therefore the broad aspect ,of the invention includes all alternative uses.

A principal object of my invention is to provide an improved proportioning control system embodying ow restricting orices in the conduits of the system, whereby the physical phenomena associated with such structure may be utilized to automatically control the flow of one uid stream in relation to another and which is particularly suitable for automatically controlling the operations of boilers of the water coil type, whereby the delivery of fluid fuel to a boiler heating apparatus is maintained in balanced relation to the volume of make-up water delivered into the boiler.

A further object of my invention is the provision, in a proportioning control system of the type described, of means for readily varying the proportions of fluids iiowing in separate conduits.

A still further object of my invention is' the provision, ina proportioning control system of the above character, of temperature responsive means for automatically adjusting the proporticning means so as to take into account the temperature or quality of the fluid discharged from the boiler.

Other and further objects and advantages of my invention will become apparent from the following description when considered in connection With the accompanying drawings in which: Y Fig. l is a longitudinal sectional view, partly in elevation, of a proportioning control system embodying the present invention, the conduits for conducting the proportionately controlled uid streams being shown fragmentarily. l

Fig. 2 is an enlarged transverse section taken on line 2-2 of Fig. 1 to illustrate an approved manner of adjustably connecting certain of the parts together.

Fig. 3 is a longitudinal sectional View taken Vsubstantially on line 3 3 of Fig. l, and

Fig. 4 is an elevational view showing a modied arrangement for manually adjusting rthe operating levers illustrated in Fig. 1.

Referring to the drawings, there is diagrammatically illustrated an embodiment of my invention as applied to the control of fluid fuel delivinto the boiler through conduit 5, as will be hereinafter described.

Suitably mounted within the conduit 5 is an orifice fitting shown diagrammatically as a plate 8 having an orifice 9 for restricting the flow of` fluid therethrough. A similar orifice fitting I I is shown diagrammatically as mounted within the conduit 6, the said fitting having an orifice I2. As seen in Fig. 1, conduits 6 and 1 are arranged in offset relation to each other with their ends closed, as at I3 and I4 respectively. the said conduits, however, communicate with each other through a valve port I 6 which is closed by a valve I1, the said valve being operable, as hereinafter described, to permit the passage of fluid fuel from conduit 1 into conduit 6 leading to the heating apparatus of the steam generator. While for convenience the apparatus in Fig. l is illustrated as occupying a Vertical position and the fluids in conduits 5 and 6 as flowing in opposite directions these conditions may be varied in accordance with the requirements in various installations. Communicating with the interior of conduit 1 is a pipe I8 which is connected to port opening of a three-way valve, indicated generally by the numeral I9, the core of the said valve being formed with a diametrical passage 2| and a radial passage 22 connecting therewith. Communicating with another port opening in the valve I9 is a pipe 23 which functions as a drain in the present installations and as an air pressure pipe in others. Communicating with an o ppositely disposed port in the valve I9 is a pipe 24, the said pipe being in axial alignment with pipe 23. As will be understood rotation of the valve core 26 will provide Various combinations of connections between conduits I8, 23 and 24, as desired.

Pipe 24 is provided with a pressure reducing valve 26 of conventional construction. Connected to the said valve 26 is a pipe 21 having a downturned portion 28 in which is suitably interposed an orifice fitting 29, the said fitting being formed with an orifice 3l. The pipe portion 28 leads into and is connected with a pressure motor, indicated generally by thenumeral 32, the said pressure motor being employed to actuate the valve I1. The pressure motor 32 is of conventional construction and includes a diaphragm 33 clamped between housing sections 34 and 35, the section 35 being supported on a tubular member 36 which encloses the valve stem 31 connected with valve I1. The valve stem 31 is xed to the diaphragm 33 to move upwardly or downwardly therewith as the fluid pressure acting on the upward face of the diaphragm changes. A coil spring 38 is positioned Ibelow the diaphragm 33 to substantially counterbalance the weight of the parts in order to give the desired action to valve I1, under fluid pressure changes above the diaphragm 33. A fluid pressure gauge 39 is connected into pipe 21 to indicate the pressures therein.

Connected into pipe 28, at a point below the orifice plate 29, is a pipe 4I having connected therein a pressure gauge 42 and being connected, at its outer end, with a pressure operated valve in the form of a bleed valve indicated generally by the numeral 43, the said bleed valve having a conduit 44 connected thereto to conduct away any excess fluid bled from pipe 4I when the valve 46 islmoved away from its valve seat' 41. The valve 46 :is mounted on the end of -a valve stem 48 which is slideable in the end plate 49 of the bleed valve 43. The valve 4G is adapted to control the pressure in the pressure chamber of the motor valve 32 for actuating valve I1. When the valve 46 is caused to open slightly to bleed fluid out of pipe 4I, the pressure in the pressure chamber of the motor valve 32 is reduced and, consequently, the valve I1 is moved by spring 38 toward its closed position, as seen in Fig. 1, thereby to reduce vthe volume of fuel delivered from conduit 1 into conduit 6. When the valve 46 closes, the pressure in the pressure chamber of motor valve ,32- increases and therefore acts upon the diaphragm 33 to impart an opening movement to the valve I1 through the valve stern 31 vto increase'the delivery of fuel to the heater or steam generator.

Valve 46 is opened and closed in response to changes in the pressure differential of the makeup water and the fluid fuel in conduits 5 and 6, respectively, on opposite sides of their respective orifice plates 8 and I I, the pressure differential being transmitted to the valve 46 Vthrough the following mechanism: Connected to conduit4 6 by smaller pipes 5I and 52 is a diaphragmcasing, indicated generally by the numeral 53, the said casing being formed of two sections between which is suitably clamped, around its marginal edges, a flexible diaphragm 54, the said diaphragm having clamps on the central portion of its two faces supporting plates or discs 56 and 51, from the left hand side of which, as viewed in Fig. l, extends a short arm 58 adapted to move with the diaphragm 54. It is noted that the pipe 5I connects at one end into the interior of conduit 6, on the high pressure side of the orifice plate II, and, at its other end, with the space within the casing `53 on the right side of diaphragm 54, while the pipe 52 connects, at one end, with the interior of conduit 6, on the 10W pressure side of the orifice plate II, and, at its other end, with the space on the left hand side of the diaphragm 54. The direction of flow of fluid within the conduit-6 is as indicated by the arrows.

Pivotally connected, as at 59within the diaphragm casing 53 is an arm II to which, at its outer end, is fixed a shaft 62 so that movement of arm 6I about the axis of shaft 62 will effect a slight rotation of the said shaft. `As seen more clearly in Fig. 3, the upper interior wall of the diaphragm casing 53 is provided with a recess 63 to receive the end of arm 6I adjacent the end of shaft 62, this provides clearance for movement of arm 6I as the diaphragm. 54 moves. The hole through which the shaft B2 extends is larger in diameter than the said shaft, and Within the intervening space, is mounted a bearing sleeve 64 of suitable rubber or plastic material which is molded to the shaft, but .is sufficiently yieldable to permit the shaft 62 to move in response to all movements of the diaphragm 54 and yet prevent any leakage'there along-of fluid pressure from the interior to the exterior of the casing. Fixed to the outer end of the-shaft 62 to rotate therewith and disposed outside of the casing 53 is the lower end of an upwardly extending arm. 66; which as Willbe understood in Fig. l, will swing tothe right or:` left as; the diaphragm 544v moves.

Connected to conduit 5 by'pipes 61' and 68 is another'diaphragm casing, indicated generally by the numeral 69; the saidacasing, issimilar in construction to'. diaphragm casing 53 .andislikewise formed of two sectionsbetweenwhich is. suitably clampeda diaphragm 1 the` saidv diaphragm having" clamped on the central: portion of its two opposed faces supporting plates orY discs: 12 and 13 from the right hand side' of Which, asviewed inv Fig. 1, extends an arm. 14 forl movementY with thev diaphragmV 1|'. Pivotally connected to the arm 14, as at 16', and within the casing 69 is an arm. 11 which is fixed to shaftY 18 extending through t-he wall of the casing, the said shaft being provided with` asleeve. similar to thelsleeve 64,V illustrated in-.Figi 3. Fixed to the outer end of shaft 18 to` rotate. therewith andi positioned exteriorally of the casing 69 is the upper end of a downwardly extending arm 19 which, as willbe understoodv in Fig. 1, will swing tothe left' or right'as the diaphragm 1|" moves. As will be seen by reference to'Fig.. 1, vpipe 61 connects the space in the casing 69 to the left of the" diaphragm 1| with the highpressurel side of the orifice plate 8, while pipe 68 connectsv the space within the casing 69 to the' right of the' diaphragm 1 |y with the low pressure side: of the orice` plate 8. It

`will be seenA thereforethat the high pressure chamber at the left of` diaphragm 1|. is opposed to the high pressure chamber at the. right of diaphragm 54.

The diaphragm casings 53 and 69 are substantially similar in construction, except that the arm 19 is longer than arm 66. The relative. lengths of arms 19l and 66, however, may be changed as desired to meet; the requirements of various operating conditions. Arm 19 for any desired. portion of. its length is provided with a longitudinally extending central slot 8| which extendstonear the bottom endof the arm or-'may open through the bottom end if desired. Arm 66 is similarly provided for any desired portion of. its length with a slot 82. Arms 19 and 66 are pivotally connected together by an inverted T-shaped link member, indicated generally b-y the numeral 83.v The position of the T-sha-ped connection is established at the time of the installation to provide the desired proportions of lever 19. and 66. Suitable adjustments of the lever proportions may be made automatically to compensate for variations in the pressure and quality of the steam or similar ad.- justments may be made manually. The member 83 comprising two identically shaped elements 8311l and 83h spaced V by spacers 04,'the said spacers being received. within the slotsl 8|. and 8-2. The elements- 8311, and. 831) are held securely against the; spacers by suitable fastenersV 86. Sufficient clearance is; provided between the: spacersv 84 and the marginal edges of the. slots 8| and- 82 to permit longitudinal: sliding movement, as: also the slight pivotal movement. required between the parts when either of .the diaphragms 54. or 1| moves.

Pivotally connectedto the. upper end of. the upright portion of the member63, as at 31, is: a lever arm 88v fulcrumed. as. at 8,9, onan extensionv 9| projecting from al.temperaturev controlled diapliragmhousing, indicated generally by the numeral 92. The said housing includes casing elements 93 and 95|y between whichl is'fsuitably secured a diaphragm 96, the said diaphragm being provided with plates or discs 91 centrallyl disposed and from whichV projects an arm 98, the said arm extends upwardly through an opening in s casing section 93: and is pivotally connectecaisl at 99,.to thelever'armi 88. A, tension spring |0| connects atl one;- end with. the free end: ofV lever arm 88, as. at' |02', and at the other end` to a spring tensioni.adjusting` screw |03.

ConnectedA to a port opening. in section 94lof the diaphragm casing; is ai pipe- |001 which connects at the.' other end to a. thermal expansion element |04'. Theexpansion element |'04Lcontains suitable medium.which is responsiveI tor temperature changes, suchv that upon the element- |04 being locatedin contact with the steam discharge conduitY .(notshown) or at other locations. Whereby itis subjected to a certain temperature,A the medium vcontained in said elementv |04 will be partially or wholly" converted to vapor Withinthe elementl and thereby increase. the pressure within the diaphragmv casing below the diaphragm 96 to-urgev the same upwardly, effectingr'an upward movement of arm 98, the degree ofV upward move-V ment.l varying. with the pressurev exerted against the diaphragm.

Also xed to thev outer end oi'shaft 18, outside of the casing 69, and adapted for rotation'- with thefshaft" 18 is an arm |06. As seen inFig'. l, the arm |06 extends angularly upwardly to a position such that' its head |01 is positioned over the valve stem. 48 and isY connected thereto to move therewith.. A bracket |08 isi mounted on the casing` 69 and serves to secureone end of the tension spring |09, the otherl end of'whichis connected to the other end ofi' the arm'` |06. The spring' |09, thus normally, tends to urge the arm l |06 in a counter-clockwise direction, as viewed in Fig. 1, exceptl as prevented by diaphragm 1|. Movement of the diaphragm 15| to the. right, through arms 14 and.11 and shaft18, would cause arm |06 to movevv in a-clockwi'se directionY andjto close the bleed valve 46` against thel tension; of spring |09.

Thev manually operated control mechanism illustrated in Fig. 4 maybe substituted for the lever 88 and the automatic adjusting means associated therewith in. Fig; l. It. includes an L- lshaped member on theupright leg'of which is pivoted a lever arm H2, the said arm t2? correspondsto` arm 88v ofv Fig.l l-and is adapted for connectionat one end to member 83. The-other end of the arm |12 is provided with a springl |3 which is attached on?` the horizontal'- legr ofv the member and is adapted to urge the arm.. |2 in. a.. clockwise direction. A screw i4 bearing againsttthefb'ottomside. ofv the: arm. I |2 serves to effect adjustment; inthe: positioningofV thee arm ||2 andto hold the same in. an adjusted position, theA lever arm |'|2 effecting'movement of they member 83 tov vary the; proportions. of the lever ratio'. of. levers 1.9. and 66.

The operation of the. present proportioning control system is as follows:

Assuming that' the inflow of water through conduit 5 is in the direction of theA arrow or to the right as'vewed in Fig. I, and' theflowi oi fluid fuel, for example gas or oil throughl the conduits 6 and 1 is in the directionofftheA arrow-or to the left, because: of theorilce plate 8: in. conduit 5', there is a. loss in pressure head in the conduit from the. upstream and'downstream sides of the orifice plate'8. As: av result,. thepressure on the left hand: side oi theorifice plate 8 is greater than that on the right hand. side. Correspond'- ingly, the pressure on the righthand` sidey of the orice plate in conduit 6 will be: greaterthan the pressure; of. the* left hand; side thereof.4 .It is thus seen that the.` pipes, 5| and; B1' lead the fhigher pressures to their respective sides ofthe daphragms 54 and 1I, and the pipes 52 and 68 'lead the lower pressures to the respective sides v,of these diaphragms.

Accordingly, the effective pressure on each of the diaphragms 54 and 'il will be the differential between the .pressure on the two sides of the orifice plates I l and 6.

Assuming a condition in which there is a flow of water in conduit corresponding to a demand `for steam, the diaphragm 1| will be flexed to the right, as viewed in Fig. 1, thereby effecting a swinging of the arms 19 and |06 in a clockwise direction. Arm |06 will thus close the bleed -valve 46 which closing will result in a. rise in the pressure in pipes 28 and 4| which pressure in :turn will act on the diaphragm 33 of the valve Vmotor 32 to ex the same downwardly to further open the valve Il (which under the conditions assumed normally stands part way open) and admit a greater volume of fuel from conduit 1 (connected to any suitable fuel pressure supply at any desired pressure) into the conduit 6, thereby increasing the pressure in conduit 6 and correspondingly increasing the amount of fuel ,owing through the orice I2 to the re cham- -ber of the steam generator. As the pressure in vconduit 6 increases, the pressure differential on opposite sides of the orice plate Il correspondingly increases, and it will finally reach a point where it is sufficient to ex diaphragm 54 to the left, as viewed in Fig. 1, and through the arms 58, 6|, 66 and member 83 effect a counterclockwise rotation of the arms 19 and HIS to open the bleed valve 46 and relieve some of the pressure in the pipe lines 4l and 28. This in turn will proportionately move valve l1 in a direction :to close and, therefore, will admit less fuel into or hot water from the boiler and functionsrconcurrently with the pressure responsiveapparatus to adjust the proportioning means in relation to the temperature of the steam or other fluid vdischarged from the boiler. As the temperature of the steam or hot water increasea'the media contained within the thermal expansion element |04 is caused to vaporize, thereby effecting an increase in pressure within the element |04 and the pipe Il, the pressure acting on the diaphragm 96 to move the arm 98 upwardly and to rock the lever arm 88 in a counter-clockwise direction. The lever 68 at the connection B1 moves downwardly in an arc having the pivot 89 as its center and therefore acts on the member 83 to incline the same in a counter-clockwise direction, thereby to rock the arms i9 and |06 in a clockwise direction to increase the opening of the bleed valve 46 which results in reducing the pressure in the .pipes 28 and 4|. Thus, the valve l1 is caused to move toward its closing position to admit a reduced volume of fuel from conduit 1 into conduit 6, thereby reducing the amount of fuel flowing through conduit 6 to the fire chamber of the steam generator.

It will be apparent that the operation of the temperature control mechanism interacts with the pressure responsive mechanism with each operating concurrently to* proportionately regu- `late the delivery offuel in relation to the inow of feed water. Thus, one control mechanism acts as a check against the other, thereby providing an added factor of safety in the operation of the steam generator.

While certain proportions and positioning of the parts have been shown in the drawings it is to be understood that this is only for illustrative purposes and that various adjustments may be made to meet the requirements of a particular installation. For example, the member V33 may be adjusted longitudinally of the arms 66 and 19 as desired to change the ratio of the movements of the respective levers.V It is accordingly apparent that by suitable adjustment of the member 83 on the arms 66 and '19, the inflow of fuel may be proportioned with relation to the inflow vof make-up water. It is also understood that any suitable means such as a pump, injector or other conventional means may be used as desired to force the incoming'water through conduit into the steam generator against the internal pressure therein so that the full pressure within the generator will not be exerted against the incoming water. As will be understood, itis the differential in pressure on the two sides of the orifice plate 8 in conduit 5 that is effective to cause movement of diaphragm 1l, and the differential in pressure on the opposite sides of orifice plate Ii in conduit 6 that is effective to cause movement of diaphragm 54.

I claim:

l. A boiler control system for proportionatelyl controlling the delivery of fluidY fuel to the fire chamber of the boiler in relation to the delivery of feed water to the boiler comprising a conduit for delivering said fuel, a conduit for delivering said feed water, inter-connected pressure operated means responsive to variations in the ow of feed water through its conduit in relation to the flow of fuel through itsV conduit, a fluid pressure operated admission valve for controlling the delivery of fuel through the fuel conduit to the re chamber of the boiler, and means actuated by said inter-connected pressure operated means for varying the uid pressure for operating said fuel admission Valve.

2. A 'boiler control system for proportionately controlling the delivery of uid fuel to the heating apparatus for the boiler in relation to the delivery of feed water to the boiler comprising a conduit for delivering said fuel to the heating apparatus, a conduit for delivering feed Water into the boiler, inter-connected pressure operated means responsive to variations in the flow of said feed water through its conduit in relation `to the 'ow of fuel through the fuel delivery conduit and including a movable member responsive to the ow of said feed water through said'feed water conduit, a movable member responsive to the flow of fuel through the fuel conduit, a set of proportioning levers connected one to each of said movable members and to each other, a fluid pressure operated admission valve for vcontrolling the delivery of fuel to the re chamber of the boiler, and means actuated by said inter-connected proportioning levers for varying the fluid pressure for operation of said fuel admission said feed Water, inter-connected pressure operated means responsive to variations in the flow of feed water through its lconduit in relation to the flow of fuel through the fuel delivery conduit and including a movable member responsive to the fiow of feed water to the boiler, a movable member responsive to the now of fuel, a set of proportioning levers connected one to each of said movable members and to each other, a fluid pressure operated admission valve for controlling the delivery o-f fuel, and a bleed valve actuated by said inter-connected proportioning levers for varying the fluid pressure for operating said fuel admission valve.

4. A boiler control system according to claim 3 in which each of said movable members is a flexible diaphragm.

5. A boiler control system according to claim 4 in which each conduit is provided With a flow restricting orice fitting therein, and the spaces on the opposite sides of each of said diaphragms are connected to the inside of their respective conduit on opposite sides of the orifice fitting therein.

6.`A boiler proportioning control system comprising a first conduit for delivering a stream of fluid into the generator, a second conduit for delivering another stream of uid into the generatoran admission valve for increasing and decreasing the flow of uid in one of said conduits, a movable member responsive to the movement of fluid in the first conduit, a movable member responsive to the temperature of the boiler, a movable member responsive to the fluid movement in the second conduit, proportioning levers connected to each of said movable members and to each other, and means operatively connected to one of said levers for controlling the position of said valve to regulate the flow of one of said streams proportionately to the flow of the other of said streams.

7.` A proportioning -control system for proportioning the flow of a stream of fluid into a steam generating apparatus with relation to the flow of a stream of fluid fuel thereto, comprising, a first conduit through which one of said streams is conducted under pressure, a second conduit through which the other of said streams is conducted `under pressure, an admission valve for varying the supply of fluid to one of said conduits, a ow restricting orifice fitting in each of said conduits, a pair of diaphragm casings, one for each conduit, each casing having a flexible diaphragm therein with a space on each side of the diaphragm, each of said diaphragm casings being connected with its respective conduit with a pair of passage Ways, one leading from one side of the orifice fitting to one side of the diaphragm, and the other from the other side of the orifice fitting to the other side of the diaphragm, each of said casings having an inside lever arm and an outside lever arm operated by the diaphragm, means connected with one of said diaphragms for controlling the position of said admission valve, means for automatically adjusting the relative proportions of said outside lever arms comprising a link adjustably connecting said outside lever arms together, a thermal expansion element associated and connected to a diaphragm casing having a flexible diaphragm therein, and-means operatively connecting the last mentioned diaphragm with said link to vary its position between said outside lever arms.

8. A proportioning control system for proportioning the flow of a stream of fluid :fuel into a,

ings being connected with its respective conduit with a pair of passage ways, one leading from one side of the orifice fitting to one side of the diaphragm, and the other from the other `side of the orifice fitting to the other side of the diaphragm, each of said casings having an inside lever arm and an outside lever arm operated by the diaphragm, means connected with one of said diaphragms for controlling the position of said admission valve, means for automatically adjusting the relative proportions of said outside lever arms comprising a link-,adjustably connecting said outside lever arms together, a thermal expanson element connected to a diaphragm casing having a iiexible diaphragm therein, lever means for connecting the last mentioned diaphragm with said link, and manual means for adjusting the position of the last mentioned lever to vary the position of said link relative to said outside lever arms.

9. A boiler proportioning control system for proportioning the flow of fluid fuel to the re chamber of the boiler with relation to the delivery of feed water to the boiler, comprising a first pipe through which said feed water is delivered to the boiler, a second pipe through which the fuel is delivered to the fire chamber, an orifice wall in each of said pipes and having a restricted orice therethrough, a diaphragm casing associated with each of said pipes, each of said casings having a diaphragm dividing the interior thereof into two spaces, a passageway connecting one of said spaces with the interior of the associated pipe on one side of its orifice wall and a passageway connecting the other one of said spaces with the interior of the associated pipe on the other side of its orifice wall, a shaft rotatably mounted in each of said casings and extending from the inside to the outside thereof, an inside lever arm in each of said casings connected at one end with a diaphragm and fixed at its other end to rotate said shaft, an outside leverarm on each of said casings and fixed to its shaft so that movement of each diaphragm will cause movement of its-outside ,lever arm, a link inter-connecting said outside lever arms and movable lengthwise thereof to vary their effective leverage ratios, and a thermal expansion element responsive to the boiler temperature and operatively connected to said link to adjust its position relative to said outside levers.

ALICK CLARKsoN.

References Cited in the le of this patent UNITED STATES PATENTS Numberk Name Date f 1,721,800 Wunsch July 23,1929 2,006,035 Stewart f June v25, 1935 2,193,095 Harrison Mar. 12, 1940 2,196,316 Long Apr. 9, 1940 2,305,070 Butler Dec. 15, 1942 

